Depletion Mode MOSFET Power Supply

Abstract

A low current power supply circuit is described that includes a depletion mode metal-oxide-semiconductor field-effect transistor (MOSFET) having a gate, a source and a drain. The drain is connectable to a power source and the source provides an output voltage for the power supply. A zener diode is connected to the gate of the depletion mode MOSFET configured to operating in its break down mode. A resistor is connected between the source and the gate of the depletion mode MOSFET and is operable to limit current to the zener diode such that the zener diode is kept in a breakdown state during operation. An output capacitor connected between the output voltage and ground.

What is claimed is: 
     
         1 . A power supply circuit comprising:
 a field effect transistor (FET) having a gate, a source and a drain, wherein the drain is connectable to a power source and the source provides an output voltage for the power supply;   a zener diode having an anode and a cathode, the cathode of the zener diode connected to the gate of the FET; and   a resistor connected between the source and the gate of the FET, the resistor operable to limit current to the zener diode such that the zener diode is kept in a breakdown state during operation.   
     
     
         2 . The power supply of  claim 1  further comprising a capacitor connected between the source of the FET and ground, the capacitor operable to handle any fluctuations in load voltage and current draw at the output voltage. 
     
     
         3 . The power supply of  claim 1  wherein the FET is a metal-oxide-semiconductor field-effect transistor (MOSFET). 
     
     
         4 . The power supply of  claim 3  wherein the MOSFET is a depletion mode MOSFET. 
     
     
         5 . The power supply of  claim 1  wherein the power supply is a direct current power supply. 
     
     
         6 . The power supply of  claim 5  wherein the DC power supply is a battery. 
     
     
         7 . The power supply of  claim 6  wherein the battery is a vehicle battery. 
     
     
         8 . The power supply of  claim 1  wherein the power supply is a alternating current power supply. 
     
     
         9 . The power supply of  claim 1  wherein the power supply is a combination of a direct current power supply and an alternating current power supply. 
     
     
         10 . The power supply of  claim 1  wherein the output voltage is 3.3 volts. 
     
     
         11 . A power supply circuit comprising:
 a depletion mode metal-oxide-semiconductor field-effect transistor (MOSFET) having a gate, a source and a drain, wherein the drain is connectable to a power source and the source provides an output voltage for the power supply;   a zener diode having an anode and a cathode, the cathode of the zener diode connected to the gate of the depletion mode MOSFET and the anode connected to a ground;   a resistor connected between the source and the gate of the depletion mode MOSFET, the resistor operable to limit current to the zener diode such that the zener diode is kept in a breakdown state during operation; and   an output capacitor connected between the output voltage and ground.   
     
     
         12 . The power supply of  claim 11  wherein the output capacitor is operable to handle any fluctuations in load voltage and current draw at the output voltage. 
     
     
         13 . The power supply of  claim 11  wherein the power supply is a direct current power supply. 
     
     
         14 . The power supply of  claim 13  wherein the DC power supply is a battery. 
     
     
         15 . The power supply of  claim 14  wherein the battery is a vehicle battery. 
     
     
         16 . The power supply of  claim 11  wherein the power supply is a alternating current power supply. 
     
     
         17 . The power supply of  claim 11  wherein the power supply is a combination of a direct current power supply and an alternating current power supply. 
     
     
         18 . The power supply of  claim 11  wherein the output voltage is 3.3 volts. 
     
     
         19 . The power supply of  claim 11  wherein the power supply is used to supply low voltage DC to operate a switching DC-DC converter incorporating an output FET switch that can operate from the high input voltage.